Field of the Invention
The present invention relates generally to electronic packaging, and more particularly to white, thin/low profile packaging having multiple emitters.
Description of the Related Art
Light emitting diodes (LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. When a bias is applied across the doped layers, holes and electrons are injected into the active layer where they recombine to generate light. Light is emitted from the active layer and from all surfaces of the LED.
In recent years, there have been dramatic improvements in LED technology such that LEDs with increased brightness and color fidelity, smaller footprints, and overall improved emitting efficiency have been introduced. LEDs also have an increased operation lifetime compared to other emitters. For example, the operational lifetime of an LED can be over 50,000 hours, while the operational lifetime of an incandescent bulb is approximately 2,000 hours. LEDs can also be more robust than other light sources while consuming less power. For these and other reasons, LEDs are becoming more popular and are now being used in more and more applications that have traditionally been the realm of incandescent, fluorescent, halogen and other emitters.
Due at least in part to these improved LEDs and improved image processing technology, LEDs can be used as the light source for a variety of display types. In order to use LED chips in these types of applications, it is known in the art to enclose one or more LED chips in a package to provide environmental and/or mechanical protection, color selection, light focusing and the like. An LED package also includes electrical leads, contacts or traces for electrically connecting the LED package to an external circuit. The LED packages are commonly mounted on a printed circuit board (PCB).
Different LED packages can be used as the light source for displays, both big and small. Large screen LED-based displays are becoming more common in many indoor and outdoor locations, and smaller screen LED-based displays such as televisions, gaming machines, screens for handheld devices, and computer monitors are becoming more common in many homes, businesses, and mobile devices. These LED-based displays can comprise thousands of “pixels” or “pixel modules”, each of which can contain a plurality of LEDs. The pixel modules can use high efficiency and high brightness LEDs that allow the displays to be visible from various distances and in a variety of environmental lighting conditions.
Most conventional LED based displays are controlled by a computer system that accepts an incoming signal (e.g. TV signal), and based on the particular color needed at the pixel module to form the overall display image, the computer system determines which LED(s) in each of the pixel modules is to emit light and how brightly. Conductors are provided to apply the appropriate power signal to each of the LEDs in the pixel modules. A power system can also be included that provides power to each of the pixel modules; the power to each of the LEDs can be modulated so light is emitted at the desired brightness.
The pixel modules can have as few as three or four LEDs that allow the pixel to emit many different colors of light from combinations of red, green, blue, and/or sometimes yellow light. For the display to show accurate and high quality images, the light emitted from the LEDs within each pixel module should be effectively mixed to provide a desired color. Moreover, each individual LED in a module and its respective emissions should not be readily and individually visible when a pixel module is illuminated via light emitting from one or more of its LEDs.
Thin, flat panel displays and/or small panel displays are becoming more common in both indoor and outdoor applications. As the popularity of flat and/or small panel displays rises, LED packages incorporated into such displays have necessarily become thinner/lower profile and smaller than their predecessors. The thin/low profile packages and/or small packages are expected to maintain their structural integrity during manufacture and use, but the integrity of such packages can become compromised. For example, the package structures can become deformed during the reflow process or damaged during the cutting process. Furthermore, packages may experience separation between the package casing and the bonding pads during manufacture and use.